by Rebecca Bryan

Indian Wells, California - Caroline Wozniacki has booked a quarter-final berth at the BNP Paribas Open as defending champion Vera Zvonareva joined the list of former champions bowing out.

Wozniacki, the charismatic Danish teenager who is seeded second, survived a see-saw battle with Russian veteran Nadia Petrova to win 6-3, 3-6, 6-0.

Wozniacki turned up the heat in the third set, surrendering only three points on her own serve as she set up a challenging quarter-final clash with Australian Open semi-finalist Zheng Jie of China - a 6-3, 4-6, 7-6 (7/1) winner over Australian Alicia Molik.

"It was a match where it just went up and down quite a bit," Wozniacki said. "It was not really a great rhythm there. I didn't feel the ball very well."

Wozniacki, who shot to prominence with her run to the US Open final in 2009, is the highest seed remaining after the second-round exit of top-seeded Svetlana Kuznetsova.

Third-seeded Victoria Azarenka was another early casualty, along with former champions Maria Sharapova, Kim Clijsters, Justine Henin, Daniela Hantuchova and Ana Ivanovic.

Zvonareva, the last of six former winners left in the draw, was toppled by eighth-seeded Australian Samantha Stosur 6-2, 7-5.

Stosur, 25, stretched her winning streak against the Russian to four matches as she continued to improve on her previous best Indian Wells showing. She had never before made it past the third round.

Stosur, who reached her first quarter-final of 2010, will next meet Spain's Maria Jose Martinez Sanchez, who beat Belgian Yanina Wickmayer 6-4, 6-4.

Fourth-seeded Elena Dementieva of Russia and fifth-seeded Agnieszka Radwanska of Poland lined up a quarter-final clash with no-nonsense victories over a pair of French opponents.

Dementieva beat Aravane Rezai, 6-3, 6-3 while Radwanska downed Marion Bartoli 6-3, 6-2.

Sixth-seeded Serbian Jelena Jankovic, who struggled mightily in a third-round victory over Sara Errani, turned in a strong performance in a 6-2, 6-2 triumph over Israel's Shahar Peer.

"I think today I played real well," Jankovic said. "I played really aggressively.

"I had a tough match last night, so I didn't know how I was going to hold up physically. And Shahar Peer is a really dangerous opponent. She can play really, really well, and she's a fighter."

In the quarter-finals, Jankovic will play Alisa Kleybanova, who beat Spain's Carla Suarez Navarro 2-6, 7-6 (7/2), 6-4

Both Jankovic and Wozniacki said it wouldn't pay to assume the spate of upsets would make their paths easier.

"Doesn't matter," Jankovic said. "You still have to beat those players who are on the other side of the net. Doesn't matter who it is. It's never easy." - AFP